A climate-control system provides heating and/or cooling to a passenger cabin of a vehicle. The climate-control system may operate to cool the passenger cabin by transporting a refrigerant through a heat cycle to absorb heat from the passenger cabin and expel the heat from the vehicle, combined with fans, blowers, and ducts to move air between the passenger cabin and the climate-control system. The climate-control system may operate as a radiator for an engine of the vehicle to heat the passenger cabin by transferring some waste heat from the engine into the passenger cabin.
Cooling and heating the passenger cabin can decrease the fuel economy of the vehicle. To cool the passenger cabin, the climate-control system takes power from the engine to move the refrigerant through the heat cycle via a compressor, condenser, fans, and so on. To heat the passenger cabin, the climate-control system may not have access to sufficient waste heat from the engine if, for example, the vehicle is an electric or hybrid-electric vehicle or if the engine has not had enough time to warm up. In those cases, the climate-control system needs additional power to heat the passenger cabin, for example, by using an electric heater, affecting fuel economy.